Cutting tool and cutting insert therefor

ABSTRACT

A cutting tool has a cutting insert retained within an insert pocket of an insert holder by a retaining screw. Spaced apart first insert rear abutment surfaces abut spaced apart first pocket rear abutment surfaces, a second insert rear abutment surface abuts a second pocket rear abutment surface, and spaced apart insert lower abutment surfaces abut spaced apart pocket lower abutment surfaces. The cutting insert has a first dimension taken between extremities of the insert side surfaces, a second dimension taken between extremities of the insert upper and lower surfaces, and, a fourth dimension taken between the insert lower abutment surfaces and the insert upper surface. The size ratio between the fourth dimension and the second dimension is in the range of 0.2 to 1, and, preferably, in the range of 0.55 to 0.6. The size ratio between the first dimension and the second dimension is in the range of 1 to 2.

FIELD OF THE INVENTION

The present invention relates to cutting tools of the type in which acutting insert is retained in an insert pocket of an insert holder bymeans of a retaining screw for performing a shaving operation.

BACKGROUND OF THE INVENTION

In cutting tools for grooving, turning or parting-off, and in cuttingtools for rotary slot cutting, a cutting insert is often retained in aninsert pocket between two generally opposing jaws. In these tools, chipsflowing from the cutting insert's cutting edge along its rake surfaceduring a cutting operation may engage the jaw adjacent the rake surfaceand subject it to considerable abrasive wear. This disadvantageouseffect will in time reduce the jaw's ability to retain the cuttinginsert within the insert pocket.

One solution which significantly overcomes this disadvantageous effectis disclosed in U.S. Pat. No. 5,947,648 to Friedman et al. A tool holderincludes a holder blade having an upper jaw and a base jaw wherein theupper jaw is fitted with an exchangeable head material shield insert forprotecting it against wear. However, this introduces additionalmaintenance of the tool.

Another solution is disclosed in U.S. Pat. No. 7,090,443 B2 to Hecht. Acutting insert is retained in an insert pocket of a cutting tool bymeans of a retaining screw. The lower surface of the cutting insertcomprises a pair of insert lower faces which extend rearwardly from theforward surface at an external non-acute insert lower angle to eachother. The lower abutment surface of the insert pocket comprises a pairof lower faces which extend forwardly from the pocket recess at aninternal holder lower angle to each other. The internal holder lowerangle is equal or slightly smaller than the external insert lower angle.

Lateral stability of the cutting insert relative to the insert holder isprovided by the lower and rear surfaces of the cutting insert havinggenerally V-shape concave (or convex) cross sections, which matecorresponding generally V-shape convex (or concave) cross sections ofthe lower and rear abutment surfaces of the insert pocket.

There are several types of shaving tools in the market. A first kind ofshaving tool is made of a solid block of HSS that is retained by adedicated mechanism. The hardness and tool life of such a tool may belimited for some applications.

Another kind of shaving tool is made of a solid block of cementedcarbide that is retained by a dedicated mechanism. Despite theadvantages of using a cemented carbide block, it is relatively expensiveand requires re-grinding after becoming worn.

Another kind of shaving tool comprises a cemented carbide flat platethat is retained in position by a clamping arm. Such kind of toolrequires a time consuming process of alignment in position. Furthermore,after becoming worn, the plate has to be re-grinded and than bere-aligned in its position.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a cuttinginsert comprising:

an insert forward surface, an opposing insert rear surface and an insertperipheral surface extending therebetween, the insert peripheral surfacecomprising two opposing insert side surfaces that extend between aninsert upper surface and an opposing insert lower surface, the insertupper surface and the insert lower surface forming insert end surfaces,

a through bore having a bore axis and extending between the insertforward and rear surfaces,

a forward cutting edge formed at an intersection of the insert uppersurface and the insert forward surface;

-   -   the insert rear surface comprising:

a first portion located between the through bore and the insert lowersurface, the first portion comprising an insert engaging element thatextends in a direction between the insert end surfaces and comprises twospaced apart first insert rear abutment surfaces, and

a second portion located between the through bore and the insert uppersurface, the second portion comprising a second insert rear abutmentsurface;

-   -   the insert lower surface comprising:

an insert lower central portion adjacent the insert engaging element,and

a pair of insert lower flanks extending from the insert lower centralportion to the insert side surfaces, each of the insert lower flanksbeing provided with an insert lower abutment surface.

According to a general overview of the cutting insert, the cuttinginsert has a first dimension taken between extremities of the insertside surfaces,

a second dimension taken between extremities of the insert upper surfaceand the insert lower surface,

a third dimension taken between extremities of the insert forwardsurface and the insert rear surface,

a fourth dimension taken between the insert lower abutment surfaces andthe insert upper surface, and

a size ratio between the fourth dimension and the second dimension is inthe range of 0.2 to 1.

Typically, the size ratio between the fourth dimension and the seconddimension is in the range of 0.55 to 0.6.

If desired, the size ratio between the first dimension and the thirddimension is in the range of 2.5 to 3.5.

Further if desired, the size ratio between the first dimension and thesecond dimension is in the range of 1 to 2.

Preferably, the two first insert rear abutment surfaces make an insertengaging angle with each other.

Advantageously, the insert engaging angle is obtuse.

Typically, the insert engaging angle is in the range from 90° to 150°.

If desired, the second insert rear abutment surface comprises twospaced-apart co-planar portions.

Further if desired, the second insert rear abutment surface is separatedfrom the through bore by an insert rear intermediate surface.

According to some embodiments, the second insert rear abutment surfacecomprises a single continuously extending surface which extends across awidth of the insert rear surface.

If desired, the second insert rear abutment surface is elevated from aninsert rear intermediate surface with respect to the insert forwardsurface, the insert rear intermediate surface being located between thesecond insert rear abutment surface and the insert lower surface.

Further if desired, the second insert rear abutment surface is ground.

Typically, each of the insert lower abutment surfaces merges with anadjacent insert side surface.

Advantageously, the insert lower abutment surfaces are co-planar.

Further advantageously, the insert lower abutment surfaces form an acuteinternal insert lower angle with the second insert rear abutmentsurface.

Further in accordance with the present invention there is provided acutting tool comprising an insert holder having an insert pocket with acutting insert seated therein, wherein:

the insert holder comprises:

-   -   a holder upper surface connecting at opposite ends to a pair of        holder side surfaces;

the insert pocket comprises:

a pocket rear surface, an upper portion of the pocket rear surfacemerging with the holder upper surface, side extremities of the pocketrear surface merging with the holder side surfaces,

a pocket threaded bore formed in the pocket rear surface and extendingrearwardly into the insert holder, the pocket threaded bore having athreaded bore axis,

a pocket engaging element formed in a lower portion of the pocket rearsurface and extending in an opposite direction from the holder uppersurface, the pocket engaging element having two spaced apart firstpocket rear abutment surfaces,

a second pocket rear abutment surface formed in an upper portion of thepocket rear surface, the second pocket rear abutment surface mergingwith the holder upper surface and with the adjacent holder side surface,

spaced apart pocket lower abutment surfaces located at opposite sides ofthe pocket threaded bore, each of the pocket lower abutment surfacesextending transversely to the upper portion of the pocket rear surfaceand merging with the holder side surfaces;

the cutting insert comprises:

-   -   an insert forward surface, an opposing insert rear surface and        an insert peripheral surface extending therebetween, the insert        peripheral surface comprising two opposing insert side surfaces        that extend between an insert upper surface and an opposing        insert lower surface, the insert upper surface and the insert        lower surface forming insert end surfaces,    -   a through bore having a bore axis and extending between the        insert forward and rear surfaces,    -   a forward cutting edge formed at an intersection of the insert        upper surface and the insert forward surface;    -   the insert rear surface comprising:

a first portion located between the through bore and the insert lowersurface, the first portion comprising an insert engaging element thatextends in a direction between the insert end surfaces and comprises twospaced apart first insert rear abutment surfaces, and

a second portion located between the through bore and the insert uppersurface, the second portion comprising a second insert rear abutmentsurface;

-   -   the insert lower surface comprising:

an insert lower central portion adjacent the insert engaging element,and

a pair of insert lower flanks extending from the insert lower centralportion to the insert side surfaces, each of the insert lower flanksbeing provided with an insert lower abutment surface;

the first insert rear abutment surfaces abut the first pocket rearabutment surfaces,

the second insert rear abutment surface abuts the second pocket rearabutment surface, the insert lower abutment surfaces abut the pocketlower abutment surfaces, and

a retaining screw passes through the through bore and threadinglyengages the pocket threaded bore.

According to some embodiments, the pocket engaging element is a pocketrecess.

Preferably, the first pocket rear abutment surfaces make a pocketengaging angle with each other.

Advantageously, the pocket engaging angle is obtuse.

Typically, the pocket engaging angle is in the range from 90° to 150°.

If desired, the second pocket rear abutment surface comprises twospaced-apart co-planar portions.

Further if desired, the pocket lower abutment surfaces are co-planar.

According to some embodiments, the pocket lower abutment surfaces areslanted at an acute pocket lower abutment angle with respect to thesecond pocket rear abutment surface.

Typically, the pocket lower abutment angle is in the range from 70° to90°.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show how thesame may be carried out in practice, reference will now be made to theaccompanying drawings, in which:

FIG. 1 is a perspective view of a cutting portion of a cutting tool inaccordance with the present invention;

FIG. 2 is a side view of the cutting tool of FIG. 1 with respect to aworkpiece being shaved;

FIG. 3 is a front perspective view of the cutting portion of FIG. 1 withthe cutting insert removed from its pocket;

FIG. 3A shows a bottom rear perspective view of another embodiment ofthe cutting insert;

FIG. 4 is a bottom rear perspective view of the cutting insert of FIG.3;

FIG. 4A shows a front perspective view of another embodiment of theinsert holder;

FIG. 5 is a side view of the cutting insert of FIG. 3;

FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 8;

FIG. 7 is a front view of the cutting portion of the insert holder ofFIG. 3;

FIG. 8 is a rear view of the cutting insert of FIG. 3;

FIG. 9 is a front view of the cutting portion of the cutting tool ofFIG. 1;

FIG. 10 is a cross-sectional view taken along line X-X in FIG. 9; and

FIG. 11 is a cross-sectional view taken along line XI-XI in FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

Attention is first drawn to FIG. 1 showing a preferred embodiment of acutting portion of a cutting tool 10 in accordance with the presentinvention. The cutting tool 10 is designed to operate as a shaving tool.Nevertheless, the cutting tool 10 may be used for other cuttingoperations such as grooving, turning and slot milling. The cutting tool10 comprises an insert holder 12 in the form of a rectangular blade witha cutting insert 14 retained in an insert pocket 16 by means of aretaining screw 18. The cutting insert 14 is typically manufactured byform-pressing and sintering carbide powders or by injection moldingtechniques.

The cutting tool 10 comprises a cutting portion 20 which includes thecutting insert 14, the insert pocket 16, and the immediate vicinity ofthe insert holder 12 adjacent the insert pocket 16. It should be notedthat directional terms appearing throughout the specification andclaims, e.g. “forward”, “rear”, “upper”, “lower” etc., are used as termsof convenience to distinguish the location of various surfaces relativeto each other. These terms are defined with reference to FIG. 1,however, they are used for illustrative purposes only, and are notintended to limit the scope of the appended claims.

FIG. 2 shows a side view of the cutting tool 10 in a typical relativeorientation with respect to a workpiece W being shaved. As shown, whenthe workpiece W rotates anticlockwise with respect to a workpiece axisof rotation C, in a direction of rotation R as shown by the curvedarrow, the cutting tool 10 moves leftward linearly in a direction shownby the straight arrow S, for shaving a thin chip, having a chipthickness T, from the workpiece W. The chip thickness T obtained in sucha shaving process is typically very thin and, practically, it may be inthe range from 0.005 mm to 0.1 mm.

Attention is drawn in addition to FIGS. 3 to 11. The construction of thecutting insert 14 will now be described. The cutting insert 14 comprisesan insert forward surface 22, an insert rear surface 24 and an insertperipheral surface 26 extending therebetween. The insert peripheralsurface 26 comprises two insert side surfaces 28 that extend between aninsert upper surface 30 and an insert lower surface 32.

The intersection between the insert upper surface 30 and the insertforward surface 22 forms a forward cutting edge 34. In the orientationshown in FIG. 2, the insert upper surface 30 serves as a rake surface ofthe cutting insert 14 and the insert forward surface 22 serves as arelief surface of the cutting insert 14. However, the cutting tool 10may be oriented in a different manner (not shown in the figures) withrespect to the workpiece W. Thus, the insert forward surface 22 mayserve as the rake surface of the cutting insert 14, in which case, theinsert upper surface 30 may serve as the relief surface of the cuttinginsert 14. The forward cutting edge 34 may have any form according tothe required shape of the machined workpiece W.

In the orientation shown in FIG. 2, the insert upper surface 30 isprovided with a forward rake angle α with respect to a first referenceplane P1 that passes through the forward cutting edge 34 and isperpendicular to the direction of linear motion S of the cutting tool10. Typically, the forward rake angle α may be in the range from 0° to15°.

The insert forward surface 22 is provided with a forward relief angle βwith respect to a second reference plane P2 that passes through theforward cutting edge 34 and is parallel to the direction of linearmotion S of the cutting tool 10. Typically, the forward relief angle βmay be in the range from 0° to 10°.

The intersection between the insert upper surface 30 and each of theinsert side surfaces 28 forms a side cutting edge 36. If required, asshown in FIG. 9, each of the side cutting edges 36 may be provided witha side relief angle γ with respect to a third reference plane P3. Thethird reference plane P3 passes through an intersection of the forwardcutting edge 34 with the side cutting edge 36 and is perpendicular tothe forward cutting edge 34. The size of the side relief angle γ variesaccording to the cutting application of the cutting tool 10. Typically,the side relief angle γ may be in the range from 0° to 5°.

The cutting insert 14 has a first dimension D1 taken between extremitiesof the insert side surfaces 28, a second dimension D2 taken betweenextremities of the insert upper surface 30 and the insert lower surface32, and, a third dimension D3 taken between extremities of the insertforward surface 22 and the insert rear surface 24. Typically, the firstdimension D1 is larger than the second dimension D2 and larger than thethird dimension D3. Further typically, the second dimension D2 is largerthan the third dimension D3. Generally, the size ratio between the firstdimension D1 and the second dimension D2 is 1 to 2. According to aspecific embodiment of the present invention, the size ratio between thefirst dimension D1 and the second dimension D2 is 1.5 to 2. Furthermore,the first dimension D1 is about three times larger than the thirddimension D3.

The cutting insert 14 is provided with a through bore 38, having a boreaxis A, that extends between the insert forward surface 22 and theinsert rear surface 24.

As best seen in FIGS. 4, 8 and 10, the insert rear surface 24 isprovided with an insert protrusion 40 that constitutes an insertengaging element. According to other embodiments of the presentinvention, the insert engaging element may be an insert recess. Theinsert protrusion 40 extends from the through bore 38 in the oppositedirection from the insert upper surface 30 and is elevated with respectto the insert rear surface 24 in the opposite direction from the insertforward surface 22.

The insert protrusion 40 is provided with a pair of first insert rearabutment surfaces 42 that are separated by an intermediate section 44.The intermediate section 44 may be a planar face and may beperpendicular to the bore axis A. The first insert rear abutmentsurfaces 42 are slightly convex as can be best seen in FIG. 10.Alternatively, the first insert rear abutment surfaces may be planarsurfaces and may make an internal insert engaging angle δ with eachother that practically may be in the range of 90° to 150°.

The insert rear surface 24 is further provided with a second insert rearabutment surface 45 which in one embodiment comprises a pair of secondinsert rear abutment surface portions 46 that are separated from thethrough bore 38 by an insert rear intermediate surface 48. The secondinsert rear abutment surface portions 46 are located distant from eachother, adjacent the insert side surfaces 28, and adjacent the insertupper surface 30. Preferably, the second insert rear abutment surfaceportions 46 are co-planar. If desired, the second insert rear abutmentsurface portions 46 may be ground.

As can be best seen in FIG. 6, the bore axis A is slanted at an internalbore slant angle λ with respect to the second insert rear abutmentsurface portions 46. Typically, the bore slant angle λ is in the rangefrom 70° to 90°. According to a specific embodiment of the presentinvention, the bore slant angle λ is 83°.

According to another embodiment of the present invention, seen in FIG.3A, the second insert rear abutment surface 45 may comprise a singlecontinuously extending insert rear abutment surface 50 that is slightlyelevated from the insert rear intermediate surface 48 with respect tothe insert forward surface 22. The continuously extending insert rearabutment surface 50 may extend across the width of the insert rearsurface 24, adjacent the insert upper surface 30. If desired, the insertrear abutment surface 50 may be ground.

The insert lower surface 32 is provided with an insert lower centralportion 52, adjacent the insert protrusion 40, and a pair of insertlower flanks 54 extending from the insert lower central portion 52 tothe insert side surfaces 28. Each of the insert lower flanks 54 isprovided with an insert lower abutment surface 56 that merges with theadjacent insert side surface 28. Preferably, the insert lower abutmentsurfaces 56 are co-planar. As seen in FIG. 11, the insert lower abutmentsurfaces 56 form an acute internal insert lower angle ω with the secondinsert rear abutment surface 45. The insert lower angle ψ may be in therange from 70° to 90°. According to a specific embodiment of the presentinvention, the insert lower angle ψ is 83°.

As shown in FIG. 8, the cutting insert 14 has a fourth dimension D4taken between the insert lower abutment surfaces 56 and the insert uppersurface 30. The fourth dimension D4 may be equal to the second dimensionD2, however, it is advantageous if the fourth dimension D4 issubstantially smaller than the second dimension D2. Thus, the size ratiobetween the fourth dimension D4 and the second dimension D2 may be inthe range of 0.2 to 1. According to a preferred embodiment of thepresent invention, the size ratio between the fourth dimension D4 andthe second dimension D2 may be in the range of 0.55 to 0.6.

Such a construction of the cutting insert 14 enables the insert lowerabutment surfaces 56 to be closer to the insert upper surface 30 thanthe first insert rear abutment surfaces 42, thus providing the cuttinginsert 14 with improved seating location, stability and repeatabilitywhen seated within an insert pocket as will be described below. Inaddition, the fourth dimension D4 is large enough to enable severalsteps of grinding of the cutting insert 14 when it is worn. According toa specific design of the cutting insert 14, it may be subjected to tensteps of grinding before it has to be disposed of. Typically, cuttinginserts are ground together as a batch in order to provide adequaterepeatability when they are replaced with each other thus eliminatingthe need to individually adjust each one of them.

The construction of the insert pocket 16 will now be described. Theinsert pocket 16 is located in a front portion 58 of the insert holder12 (see FIG. 3). The insert holder 12 has, in an upper portion thereof,a holder upper surface 60 that extends between two holder side surfaces62. A front end of the insert holder is provided with a holder frontsurface 64 that extends between the holder side surfaces 62. The insertpocket 16 has a pocket rear surface 66. An upper portion 68 of thepocket rear surface 66 merges with the holder upper surface 60. Sideextremities 70 of the pocket rear surface 66 merge with the adjacentholder side surface 62. A pocket threaded bore 72, having a threadedbore axis B, is formed in the pocket rear surface 66 and extendsrearwardly into the insert holder 12.

A lower portion 74 of the pocket rear surface 66 is provided with apocket recess 76 constituting a pocket engaging element. The pocketrecess 76 extends from the pocket threaded bore 72 in the oppositedirection from the holder upper surface 60. The pocket recess 76 has twospaced apart first pocket rear abutment surfaces 78 that may beseparated by a recess intermediate section 80. As can be best seen inFIG. 10, the recess intermediate section 80 may be a planar face and maybe perpendicular to the threaded bore axis B. The first pocket rearabutment surfaces 78 may be planar surfaces and may make an externalpocket engaging angle θ with each other that may be in the range from90° to 150°. According to a specific embodiment of the presentinvention, the pocket engaging angle θ is 120°.

The upper portion 68 of the pocket rear surface 66 is provided with asecond pocket rear abutment surface 82 which in one embodiment comprisesa pair of second pocket rear abutment surface portions 84. Each of thesecond pocket rear abutment surface portions 84 merges with the holderupper surface 60 and with the adjacent holder side surface 62.Preferably, the second pocket rear abutment surface portions 84 areco-planar. If desired, the second pocket rear abutment surface portions84 may be ground.

According to another embodiment of the present invention, seen in FIG.4A, the second pocket rear abutment surface 82 may comprise acontinuously extending pocket rear abutment surface 86 that extendsacross the width of the pocket rear surface 66 proximate the holderupper surface 60. If desired, the continuously extending pocket rearabutment surface 86 may be slightly elevated with respect to itsadjacent portion of the pocket rear surface 66.

The insert pocket 16 is further provided with pocket lower abutmentsurfaces 88 that extend transversely to the upper portion 68 of thepocket rear surface 66. The pocket lower abutment surfaces 88 may beadvantageously located spaced apart at both sides of the pocket threadedbore 72. Each of the pocket lower abutment surfaces 88 merges with theadjacent holder side surface 62. Preferably, the pocket lower abutmentsurfaces 88 are co-planar and are slanted at a pocket lower abutmentangle φ with respect to the second pocket rear abutment surface 82, ascan be best seen in FIG. 11. Typically, the pocket lower abutment angleφ is acute thus providing the cutting insert a wedge effect when seatedin its pocket. The pocket lower abutment angle φ may be in the rangefrom 70° to 90°. According to a specific embodiment of the presentinvention, the pocket lower abutment angle φ is 83°.

The cutting insert 14 is retained in the insert pocket 16 by means ofthe retaining screw 18 in the following manner. The first insert rearabutment surfaces 42 abut the first pocket rear abutment surfaces 78,the second insert rear abutment surface 45 abuts the second pocket rearabutment surface 82, and the insert lower abutment surfaces 56 abut thepocket lower abutment surfaces 88. The retaining screw 18 passes throughthe through bore 38 and threadingly engages the pocket threaded bore 72.

Thus, a very accurate and stable position of the cutting insert 14 isobtained. Furthermore, when the cutting insert 14 is worn and isreplaced by a new cutting insert, upon tightening the retaining screw 18the new cutting insert 14 is brought into the desired position, thus,adequate repeatability is obtained and further adjustment of the cuttinginsert for performing a shaving operation is unnecessary, in contrary toprior art techniques.

The abutment between the cutting insert 14 and the insert pocket 16 isnot limited to the described above and other combinations may bepossible. In one embodiment, for example, the cutting insert 14 may beprovided with the second insert rear abutment surface 45 comprising apair of second insert rear abutment surface portions 46, as shown inFIG. 4, and the insert pocket 16 may be provided with a second pocketrear abutment surface 82 comprising a continuously extending pocket rearabutment surface 86, as shown in FIG. 4A.

In another embodiment, the cutting insert 14 may be provided with asecond insert rear abutment surface 45 comprising a single continuouslyextending insert rear abutment surface 50, as shown in FIG. 3A, and theinsert pocket 16 may be provided with a second pocket rear abutmentsurface 82 comprising a pair of second pocket rear abutment surfaceportions 84, as shown in FIG. 3.

In another embodiment, the cutting insert 14 may be provided with thesecond insert rear abutment surface 45 comprising a pair of secondinsert rear abutment surface portions 46, as shown in FIG. 4, and theinsert pocket 16 may be provided with a second pocket rear abutmentsurface 82 comprising a pair of second pocket rear abutment surfaceportions 84, as shown in FIG. 3.

In another embodiment, the cutting insert 14 may be provided with asecond insert rear abutment surface 45 comprising a single continuouslyextending insert rear abutment surface 50, as shown in FIG. 3A, and theinsert pocket 16 may be provided with a second pocket rear abutmentsurface 82 comprising a continuously extending pocket rear abutmentsurface 86, as shown in FIG. 4A.

The pair of second insert rear abutment surface portions 46 may beelevated with respect to an adjacent region of the insert rear surface24. Likewise, the continuously extending insert rear abutment surface 50may be elevated with respect to an adjacent region of the insert rearsurface 24.

The continuously extending pocket rear abutment surface 86 may beelevated with respect to an adjacent region of the pocket rear surface66. Likewise, the pair of second pocket rear abutment surface portions84 may be elevated with respect to an adjacent region of the pocket rearsurface 66.

If desired, each of the abutment surfaces described above may be ground.

The first insert rear abutment surfaces 42 do not have to be spacedapart by the intermediate section 44. The intermediate section 44 may beomitted, as long as the first insert rear abutment surfaces 42 make aninternal insert engaging angle δ with each other.

The first pocket rear abutment surfaces 78 do not have to be spacedapart by the intermediate section 80. The intermediate section 80 may beomitted, as long as the first pocket rear abutment surfaces 78 make anexternal pocket engaging angle θ with each other.

Although the present invention has been described to a certain degree ofparticularity, it should be understood that various alterations andmodifications could be made without departing from the spirit or scopeof the invention as hereinafter claimed.

For example, as already mentioned, the insert engaging element may be arecess instead of a protrusion. In which case, accordingly, the pocketengaging element may be a complementary protrusion.

The first pocket rear abutment surfaces do not have to be planar andthey may have any desired shape provided for engaging with the firstinsert rear abutment surfaces.

The second insert rear abutment surface portions 46 may be provided witha recess therebetween. Likewise, the second pocket rear abutment surfaceportions 84 may be provided with a recess therebetween.

1. A cutting insert comprising: an insert forward surface, an opposing insert rear surface and an insert peripheral surface extending therebetween, the insert peripheral surface comprising two opposing insert side surfaces that extend between an insert upper surface and an opposing insert lower surface, the insert upper surface and the insert lower surface forming insert end surfaces, a through bore having a bore axis and extending between the insert forward and rear surfaces, a forward cutting edge formed at an intersection of the insert upper surface and the insert forward surface; the insert rear surface comprising: a first portion located between the through bore and the insert lower surface, the first portion comprising an insert engaging element that extends in a direction between the insert end surfaces and comprises two spaced apart first insert rear abutment surfaces, and a second portion located between the through bore and the insert upper surface, the second portion comprising a second insert rear abutment surface; the insert lower surface comprising: an insert lower central portion adjacent the insert engaging element, and a pair of insert lower flanks extending from the insert lower central portion to the insert side surfaces, each of the insert lower flanks being provided with an insert lower abutment surface.
 2. The cutting insert according to claim 1, wherein: the cutting insert has a first dimension taken between extremities of the insert side surfaces, a second dimension taken between extremities of the insert upper surface and the insert lower surface, a third dimension taken between extremities of the insert forward surface and the insert rear surface, a fourth dimension taken between the insert lower abutment surfaces and the insert upper surface, and a size ratio between the fourth dimension and the second dimension is in the range of 0.2 to
 1. 3. The cutting insert according to claim 2, wherein the size ratio between the fourth dimension and the second dimension is in the range of 0.55 to 0.6.
 4. The cutting insert according to claim 2, wherein the size ratio between the first dimension and the third dimension is in the range of 2.5 to 3.5.
 5. The cutting insert according to claim 2, wherein the size ratio between the first dimension and the second dimension is in the range of 1 to
 2. 6. The cutting insert according to claim 1, wherein the two first insert rear abutment surfaces make an insert engaging angle with each other.
 7. The cutting insert according to claim 6, wherein the insert engaging angle is obtuse.
 8. The cutting insert according to claim 7, wherein the insert engaging angle is in the range from 90° to 150°.
 9. The cutting insert according to claim 1, wherein the second insert rear abutment surface comprises two spaced-apart co-planar portions.
 10. The cutting insert according to claim 1, wherein the second insert rear abutment surface is separated from the through bore by an insert rear intermediate surface.
 11. The cutting insert according to claim 1, wherein the second insert rear abutment surface comprises a single continuously extending surface which extends across a width of the insert rear surface.
 12. The cutting insert according to claim 11, wherein the second insert rear abutment surface is elevated from an insert rear intermediate surface with respect to the insert forward surface, the insert rear intermediate surface being located between the second insert rear abutment surface and the insert lower surface.
 13. The cutting insert according to claim 12, wherein the second insert rear abutment surface is ground.
 14. The cutting insert according to claim 1, wherein each of the insert lower abutment surfaces merges with an adjacent insert side surface.
 15. The cutting insert according to claim 1, wherein the insert lower abutment surfaces are co-planar.
 16. The cutting insert according to claim 1, wherein the insert lower abutment surfaces form an acute internal insert lower angle with the second insert rear abutment surface.
 17. A cutting tool comprising an insert holder having an insert pocket with a cutting insert seated therein, wherein: the insert holder comprises: a holder upper surface connecting at opposite ends to a pair of holder side surfaces; the insert pocket comprises: a pocket rear surface, an upper portion of the pocket rear surface merging with the holder upper surface, side extremities of the pocket rear surface merging with the holder side surfaces, a pocket threaded bore formed in the pocket rear surface and extending rearwardly into the insert holder, the pocket threaded bore having a threaded bore axis, a pocket engaging element formed in a lower portion of the pocket rear surface and extending in an opposite direction from the holder upper surface, the pocket engaging element having two spaced apart first pocket rear abutment surfaces, a second pocket rear abutment surface formed in an upper portion of the pocket rear surface, the second pocket rear abutment surface merging with the holder upper surface and with an adjacent holder side surface, spaced apart pocket lower abutment surfaces located at opposite sides of the pocket threaded bore, each of the pocket lower abutment surfaces extending transversely to the upper portion of the pocket rear surface and merging with the holder side surfaces; the cutting insert comprises: an insert forward surface, an opposing insert rear surface and an insert peripheral surface extending therebetween, the insert peripheral surface comprising two opposing insert side surfaces that extend between an insert upper surface and an opposing insert lower surface, the insert upper surface and the insert lower surface forming insert end surfaces, a through bore having a bore axis and extending between the insert forward and rear surfaces, a forward cutting edge formed at an intersection of the insert upper surface and the insert forward surface; the insert rear surface comprising: a first portion located between the through bore and the insert lower surface, the first portion comprising an insert engaging element that extends in a direction between the insert end surfaces and comprises two spaced apart first insert rear abutment surfaces, and a second portion located between the through bore and the insert upper surface, the second portion comprising a second insert rear abutment surface; the insert lower surface comprising: an insert lower central portion adjacent the insert engaging element, and a pair of insert lower flanks extending from the insert lower central portion to the insert side surfaces, each of the insert lower flanks being provided with an insert lower abutment surface; the first insert rear abutment surfaces abut the first pocket rear abutment surfaces, the second insert rear abutment surface abuts the second pocket rear abutment surface, the insert lower abutment surfaces abut the pocket lower abutment surfaces, and a retaining screw passes through the through bore and threadingly engages the pocket threaded bore.
 18. The cutting tool according to claim 17, wherein the pocket engaging element is a pocket recess.
 19. The cutting tool according to claim 17, wherein the first pocket rear abutment surfaces make a pocket engaging angle with each other.
 20. The cutting tool according to claim 19, wherein the pocket engaging angle is obtuse.
 21. The cutting tool according to claim 20, wherein the pocket engaging angle is in the range from 90° to 150°.
 22. The cutting tool according to claim 17, wherein the second pocket rear abutment surface comprises two spaced-apart co-planar portions.
 23. The cutting tool according to claim 17, wherein the pocket lower abutment surfaces are co-planar.
 24. The cutting tool according to claim 17, wherein the pocket lower abutment surfaces are slanted at an acute pocket lower abutment angle with respect to the second pocket rear abutment surface.
 25. The cutting tool according to claim 24, wherein the pocket lower abutment angle is in the range from 70° to 90°. 